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// Copyright 2011 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
// Package packet implements parsing and serialization of OpenPGP packets, as
// specified in RFC 4880.
package packet
import (
"crypto/aes"
"crypto/cast5"
"crypto/cipher"
error_ "crypto/openpgp/error"
"io"
"math/big"
)
// readFull is the same as io.ReadFull except that reading zero bytes returns
// ErrUnexpectedEOF rather than EOF.
func readFull(r io.Reader, buf []byte) (n int, err error) {
n, err = io.ReadFull(r, buf)
if err == io.EOF {
err = io.ErrUnexpectedEOF
}
return
}
// readLength reads an OpenPGP length from r. See RFC 4880, section 4.2.2.
func readLength(r io.Reader) (length int64, isPartial bool, err error) {
var buf [4]byte
_, err = readFull(r, buf[:1])
if err != nil {
return
}
switch {
case buf[0] < 192:
length = int64(buf[0])
case buf[0] < 224:
length = int64(buf[0]-192) << 8
_, err = readFull(r, buf[0:1])
if err != nil {
return
}
length += int64(buf[0]) + 192
case buf[0] < 255:
length = int64(1) << (buf[0] & 0x1f)
isPartial = true
default:
_, err = readFull(r, buf[0:4])
if err != nil {
return
}
length = int64(buf[0])<<24 |
int64(buf[1])<<16 |
int64(buf[2])<<8 |
int64(buf[3])
}
return
}
// partialLengthReader wraps an io.Reader and handles OpenPGP partial lengths.
// The continuation lengths are parsed and removed from the stream and EOF is
// returned at the end of the packet. See RFC 4880, section 4.2.2.4.
type partialLengthReader struct {
r io.Reader
remaining int64
isPartial bool
}
func (r *partialLengthReader) Read(p []byte) (n int, err error) {
for r.remaining == 0 {
if !r.isPartial {
return 0, io.EOF
}
r.remaining, r.isPartial, err = readLength(r.r)
if err != nil {
return 0, err
}
}
toRead := int64(len(p))
if toRead > r.remaining {
toRead = r.remaining
}
n, err = r.r.Read(p[:int(toRead)])
r.remaining -= int64(n)
if n < int(toRead) && err == io.EOF {
err = io.ErrUnexpectedEOF
}
return
}
// partialLengthWriter writes a stream of data using OpenPGP partial lengths.
// See RFC 4880, section 4.2.2.4.
type partialLengthWriter struct {
w io.WriteCloser
lengthByte [1]byte
}
func (w *partialLengthWriter) Write(p []byte) (n int, err error) {
for len(p) > 0 {
for power := uint(14); power < 32; power-- {
l := 1 << power
if len(p) >= l {
w.lengthByte[0] = 224 + uint8(power)
_, err = w.w.Write(w.lengthByte[:])
if err != nil {
return
}
var m int
m, err = w.w.Write(p[:l])
n += m
if err != nil {
return
}
p = p[l:]
break
}
}
}
return
}
func (w *partialLengthWriter) Close() error {
w.lengthByte[0] = 0
_, err := w.w.Write(w.lengthByte[:])
if err != nil {
return err
}
return w.w.Close()
}
// A spanReader is an io.LimitReader, but it returns ErrUnexpectedEOF if the
// underlying Reader returns EOF before the limit has been reached.
type spanReader struct {
r io.Reader
n int64
}
func (l *spanReader) Read(p []byte) (n int, err error) {
if l.n <= 0 {
return 0, io.EOF
}
if int64(len(p)) > l.n {
p = p[0:l.n]
}
n, err = l.r.Read(p)
l.n -= int64(n)
if l.n > 0 && err == io.EOF {
err = io.ErrUnexpectedEOF
}
return
}
// readHeader parses a packet header and returns an io.Reader which will return
// the contents of the packet. See RFC 4880, section 4.2.
func readHeader(r io.Reader) (tag packetType, length int64, contents io.Reader, err error) {
var buf [4]byte
_, err = io.ReadFull(r, buf[:1])
if err != nil {
return
}
if buf[0]&0x80 == 0 {
err = error_.StructuralError("tag byte does not have MSB set")
return
}
if buf[0]&0x40 == 0 {
// Old format packet
tag = packetType((buf[0] & 0x3f) >> 2)
lengthType := buf[0] & 3
if lengthType == 3 {
length = -1
contents = r
return
}
lengthBytes := 1 << lengthType
_, err = readFull(r, buf[0:lengthBytes])
if err != nil {
return
}
for i := 0; i < lengthBytes; i++ {
length <<= 8
length |= int64(buf[i])
}
contents = &spanReader{r, length}
return
}
// New format packet
tag = packetType(buf[0] & 0x3f)
length, isPartial, err := readLength(r)
if err != nil {
return
}
if isPartial {
contents = &partialLengthReader{
remaining: length,
isPartial: true,
r: r,
}
length = -1
} else {
contents = &spanReader{r, length}
}
return
}
// serializeHeader writes an OpenPGP packet header to w. See RFC 4880, section
// 4.2.
func serializeHeader(w io.Writer, ptype packetType, length int) (err error) {
var buf [6]byte
var n int
buf[0] = 0x80 | 0x40 | byte(ptype)
if length < 192 {
buf[1] = byte(length)
n = 2
} else if length < 8384 {
length -= 192
buf[1] = 192 + byte(length>>8)
buf[2] = byte(length)
n = 3
} else {
buf[1] = 255
buf[2] = byte(length >> 24)
buf[3] = byte(length >> 16)
buf[4] = byte(length >> 8)
buf[5] = byte(length)
n = 6
}
_, err = w.Write(buf[:n])
return
}
// serializeStreamHeader writes an OpenPGP packet header to w where the
// length of the packet is unknown. It returns a io.WriteCloser which can be
// used to write the contents of the packet. See RFC 4880, section 4.2.
func serializeStreamHeader(w io.WriteCloser, ptype packetType) (out io.WriteCloser, err error) {
var buf [1]byte
buf[0] = 0x80 | 0x40 | byte(ptype)
_, err = w.Write(buf[:])
if err != nil {
return
}
out = &partialLengthWriter{w: w}
return
}
// Packet represents an OpenPGP packet. Users are expected to try casting
// instances of this interface to specific packet types.
type Packet interface {
parse(io.Reader) error
}
// consumeAll reads from the given Reader until error, returning the number of
// bytes read.
func consumeAll(r io.Reader) (n int64, err error) {
var m int
var buf [1024]byte
for {
m, err = r.Read(buf[:])
n += int64(m)
if err == io.EOF {
err = nil
return
}
if err != nil {
return
}
}
panic("unreachable")
}
// packetType represents the numeric ids of the different OpenPGP packet types. See
// http://www.iana.org/assignments/pgp-parameters/pgp-parameters.xhtml#pgp-parameters-2
type packetType uint8
const (
packetTypeEncryptedKey packetType = 1
packetTypeSignature packetType = 2
packetTypeSymmetricKeyEncrypted packetType = 3
packetTypeOnePassSignature packetType = 4
packetTypePrivateKey packetType = 5
packetTypePublicKey packetType = 6
packetTypePrivateSubkey packetType = 7
packetTypeCompressed packetType = 8
packetTypeSymmetricallyEncrypted packetType = 9
packetTypeLiteralData packetType = 11
packetTypeUserId packetType = 13
packetTypePublicSubkey packetType = 14
packetTypeSymmetricallyEncryptedMDC packetType = 18
)
// Read reads a single OpenPGP packet from the given io.Reader. If there is an
// error parsing a packet, the whole packet is consumed from the input.
func Read(r io.Reader) (p Packet, err error) {
tag, _, contents, err := readHeader(r)
if err != nil {
return
}
switch tag {
case packetTypeEncryptedKey:
p = new(EncryptedKey)
case packetTypeSignature:
p = new(Signature)
case packetTypeSymmetricKeyEncrypted:
p = new(SymmetricKeyEncrypted)
case packetTypeOnePassSignature:
p = new(OnePassSignature)
case packetTypePrivateKey, packetTypePrivateSubkey:
pk := new(PrivateKey)
if tag == packetTypePrivateSubkey {
pk.IsSubkey = true
}
p = pk
case packetTypePublicKey, packetTypePublicSubkey:
pk := new(PublicKey)
if tag == packetTypePublicSubkey {
pk.IsSubkey = true
}
p = pk
case packetTypeCompressed:
p = new(Compressed)
case packetTypeSymmetricallyEncrypted:
p = new(SymmetricallyEncrypted)
case packetTypeLiteralData:
p = new(LiteralData)
case packetTypeUserId:
p = new(UserId)
case packetTypeSymmetricallyEncryptedMDC:
se := new(SymmetricallyEncrypted)
se.MDC = true
p = se
default:
err = error_.UnknownPacketTypeError(tag)
}
if p != nil {
err = p.parse(contents)
}
if err != nil {
consumeAll(contents)
}
return
}
// SignatureType represents the different semantic meanings of an OpenPGP
// signature. See RFC 4880, section 5.2.1.
type SignatureType uint8
const (
SigTypeBinary SignatureType = 0
SigTypeText = 1
SigTypeGenericCert = 0x10
SigTypePersonaCert = 0x11
SigTypeCasualCert = 0x12
SigTypePositiveCert = 0x13
SigTypeSubkeyBinding = 0x18
)
// PublicKeyAlgorithm represents the different public key system specified for
// OpenPGP. See
// http://www.iana.org/assignments/pgp-parameters/pgp-parameters.xhtml#pgp-parameters-12
type PublicKeyAlgorithm uint8
const (
PubKeyAlgoRSA PublicKeyAlgorithm = 1
PubKeyAlgoRSAEncryptOnly PublicKeyAlgorithm = 2
PubKeyAlgoRSASignOnly PublicKeyAlgorithm = 3
PubKeyAlgoElGamal PublicKeyAlgorithm = 16
PubKeyAlgoDSA PublicKeyAlgorithm = 17
)
// CanEncrypt returns true if it's possible to encrypt a message to a public
// key of the given type.
func (pka PublicKeyAlgorithm) CanEncrypt() bool {
switch pka {
case PubKeyAlgoRSA, PubKeyAlgoRSAEncryptOnly, PubKeyAlgoElGamal:
return true
}
return false
}
// CanSign returns true if it's possible for a public key of the given type to
// sign a message.
func (pka PublicKeyAlgorithm) CanSign() bool {
switch pka {
case PubKeyAlgoRSA, PubKeyAlgoRSASignOnly, PubKeyAlgoDSA:
return true
}
return false
}
// CipherFunction represents the different block ciphers specified for OpenPGP. See
// http://www.iana.org/assignments/pgp-parameters/pgp-parameters.xhtml#pgp-parameters-13
type CipherFunction uint8
const (
CipherCAST5 CipherFunction = 3
CipherAES128 CipherFunction = 7
CipherAES192 CipherFunction = 8
CipherAES256 CipherFunction = 9
)
// KeySize returns the key size, in bytes, of cipher.
func (cipher CipherFunction) KeySize() int {
switch cipher {
case CipherCAST5:
return cast5.KeySize
case CipherAES128:
return 16
case CipherAES192:
return 24
case CipherAES256:
return 32
}
return 0
}
// blockSize returns the block size, in bytes, of cipher.
func (cipher CipherFunction) blockSize() int {
switch cipher {
case CipherCAST5:
return 8
case CipherAES128, CipherAES192, CipherAES256:
return 16
}
return 0
}
// new returns a fresh instance of the given cipher.
func (cipher CipherFunction) new(key []byte) (block cipher.Block) {
switch cipher {
case CipherCAST5:
block, _ = cast5.NewCipher(key)
case CipherAES128, CipherAES192, CipherAES256:
block, _ = aes.NewCipher(key)
}
return
}
// readMPI reads a big integer from r. The bit length returned is the bit
// length that was specified in r. This is preserved so that the integer can be
// reserialized exactly.
func readMPI(r io.Reader) (mpi []byte, bitLength uint16, err error) {
var buf [2]byte
_, err = readFull(r, buf[0:])
if err != nil {
return
}
bitLength = uint16(buf[0])<<8 | uint16(buf[1])
numBytes := (int(bitLength) + 7) / 8
mpi = make([]byte, numBytes)
_, err = readFull(r, mpi)
return
}
// mpiLength returns the length of the given *big.Int when serialized as an
// MPI.
func mpiLength(n *big.Int) (mpiLengthInBytes int) {
mpiLengthInBytes = 2 /* MPI length */
mpiLengthInBytes += (n.BitLen() + 7) / 8
return
}
// writeMPI serializes a big integer to w.
func writeMPI(w io.Writer, bitLength uint16, mpiBytes []byte) (err error) {
_, err = w.Write([]byte{byte(bitLength >> 8), byte(bitLength)})
if err == nil {
_, err = w.Write(mpiBytes)
}
return
}
// writeBig serializes a *big.Int to w.
func writeBig(w io.Writer, i *big.Int) error {
return writeMPI(w, uint16(i.BitLen()), i.Bytes())
}
|